Lawinenlagebericht

Northwest Mountains

Crested Butte Avalanche Center
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Lawinengefahr

Mon
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
2 · Mässig
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Kernpunkte

The close call with a very large avalanche near Marble and more explosive results at Irwin yesterday highlight the continued threat of triggering a dangerous avalanche today.   Avalanches this week have been breaking 3 to 6+ feet deep on buried weak layers in the bottom half of the snowpack, on most aspects and elevations.   Some have been unsurvivable, like this wall-to-wall slide in Red Lady Bowl.  Although the likelihood of triggering a persistent slab is gradually decreasing now that the storm is over, the potential size demands a conservative mindset.

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    2–3.5

    Slabs ranging from 3 to 6+ feet thick have formed around the compass and at all elevations over faceted weak layers in the lower snowpack.  The poor snowpack structure produced widespread activity during stormy weather in early January.  Persistent slab avalanches can propagate widely through the terrain, or be remotely triggered from low-angle slopes connected to steeper slopes.  Now the problem is becoming more difficult to trigger because the snowpack is adjusting and weak layers are hard to impact. Persistent slab avalanches can propagate widely through the terrain, or be remotely triggered from low-angle slopes connected to steeper slopes. You are most likely to trigger an avalanche from a shallow area on the slopes, such as a rock band or where wind drifting has formed variable snow depths.  Give yourself a wide margin for error given how consequential the problem is right now.   You can reliably avoid the problem by traveling on slope angles that are consistently less than 30 degrees without overhead hazards.

    1/4:  A destructive natural avalanche in Red Lady Bowl broke full width on Wednesday.  This avalanche would be hard to survive.

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–1.5

    Observers yesterday noted a number of shallow wind slabs that failed during the most recent pulse of snow and wind.  Slabs formed from westerly winds on Friday, and today's southwest winds could cause additional drifting.  Be cautious of steep slopes where you find evidence of recent drifting or cracking underfoot.   

    A shallow wind slab that released below a corniced ridgeline on Friday.  

Avalanche Discussion

Yesterday, two snowmobilers were buried and killed in an avalanche near Winter Park.  Yet another tragic accident that brings the fatality count in Colorado up to four in recent weeks.  This is a tricky snowpack folks.  Patience, patience, patience.  

Yesterday's clear skies allowed us to get a better sense of how the snowpack responded to the most recent storm, which brought up to 20" to the Northwest Mountains, and 10" or less in the Southeast Mountains.  Eric noted continued natural persistent slab activity in shallower parts of the forecast area, which fits the pattern of where we have been observing the most reactive snowpack recently.  Although shallow wind slab activity was fairly common throughout the Ruby Range and Anthracites, we didn't spot any avalanches that stepped down.  However, hand shots at Irwin continued to produce destructive avalanches that broke near the ground and snapped trees.  Skiers near Marble yesterday had a close call with a very large avalanche that wiped out parts of their skin track.  In both the Irwin and Marble avalanches, the slides were more than four feet thick, but they were triggered from shallower parts of the slab.  In the Northwest Mountains, we've lowered the likelihood to possible across all elevations.  That means there are fewer problematic slopes and those slopes are harder to trigger.  We recommend conservative travel at higher elevations, where there are more potential trigger points and where expected sizes are up to very large (D3+).  As sensitivity continues to gradually decrease, we'll see the danger gradually decrease as well.

Near and east of town, the snowpack is shallower.  Our November and December weak layers are larger and more developed because of this, and overlying slabs are thinner, making them more sensitive to human triggers.  Sensitivity is also declining but at a slower rate, and likelihood is stuck at "likely" until we can get good evidence that those thinner slabs are becoming stubborn.  That probably won't change before the next round of snowfall arrives on Tuesday, adding further stress to an already reactive structure.    

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